This type of computer system includes a host system such as a host computer on a user's side and a storage system for realizing data storage processing on the host system. The storage system includes storage units for storing data and a storage subsystem for processing data input/output requests between storage devices and the host computer.
The storage subsystem manages logical storage areas as targets of input/output from the host computer, and a controller in the storage subsystem performs processing for writing data to logical volumes and processing for reading data from logical volumes.
Some types of storage subsystems have a plurality of controllers. Such a storage subsystem makes the plurality of controllers share the processing for inputting/outputting data to/from a plurality of logical volumes in order to equalize load caused by the data processing among the plurality of controllers.
Specifically speaking, an administrator of the storage subsystem sets allocation of the controllers to take charge in processing for inputting/outputting data to/from logical volumes to a control memory for the storage subsystem before starting the operation of a data storage service.
If a load on the plurality of controllers becomes unbalanced after starting the operation of the data storage service, the storage subsystem can transfer a control and processing authority of a controller, on which the load is concentrated, over logical volumes belonging to that controller to another controller (Japanese Patent Application Laid-Open (Kokai) Publication No. 2008-269424).